Commit 5fda3f35 authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

net: make netdev_lock() protect netdev->reg_state 



Protect writes to netdev->reg_state with netdev_lock().
From now on holding netdev_lock() is sufficient to prevent
the net_device from getting unregistered, so code which
wants to hold just a single netdev around no longer needs
to hold rtnl_lock.

We do not protect the NETREG_UNREGISTERED -> NETREG_RELEASED
transition. We'd need to move mutex_destroy(netdev->lock)
to .release, but the real reason is that trying to stop
the unregistration process mid-way would be unsafe / crazy.
Taking references on such devices is not safe, either.
So the intended semantics are to lock REGISTERED devices.

Reviewed-by: default avatarJoe Damato <jdamato@fastly.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115035319.559603-3-kuba@kernel.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent ebda2f0b

include/linux/netdevice.h

+1 −1
Original line number Diff line number Diff line
@@ -2448,7 +2448,7 @@ struct net_device { 
	 * Should always be taken using netdev_lock() / netdev_unlock() helpers.

	 * Drivers are free to use it for other protection.

	 *

	 * Protects: @net_shaper_hierarchy.

	 * Protects: @reg_state, @net_shaper_hierarchy.

	 * Ordering: take after rtnl_lock.

	 */

	struct mutex		lock;

net/core/dev.c

+6 −0
Original line number Diff line number Diff line
@@ -10695,7 +10695,9 @@ int register_netdevice(struct net_device *dev) 


	ret = netdev_register_kobject(dev);



	netdev_lock(dev);

	WRITE_ONCE(dev->reg_state, ret ? NETREG_UNREGISTERED : NETREG_REGISTERED);

	netdev_unlock(dev);



	if (ret)

		goto err_uninit_notify;
@@ -10969,7 +10971,9 @@ void netdev_run_todo(void) 
			continue;

		}



		netdev_lock(dev);

		WRITE_ONCE(dev->reg_state, NETREG_UNREGISTERED);

		netdev_unlock(dev);

		linkwatch_sync_dev(dev);

	}
@@ -11575,7 +11579,9 @@ void unregister_netdevice_many_notify(struct list_head *head, 
	list_for_each_entry(dev, head, unreg_list) {

		/* And unlink it from device chain. */

		unlist_netdevice(dev);

		netdev_lock(dev);

		WRITE_ONCE(dev->reg_state, NETREG_UNREGISTERING);

		netdev_unlock(dev);

	}

	flush_all_backlogs();